The present invention relates to a drum used for galvanization or chemical processing or treatment of articles or bulk parts which are made of metal, plastics, or other raw materials.
Drums of the preceding species, are already known in the art, and such conventional drums have a variety of different designs. It has, however, been found that the manner of perforation of the covering surface or drum, as well as their inner surface structure influenced considerably the galvanization process. Thus, it has been found that the manner of perforation regulates extensively the current consumption of the galvanization or plating material within the drum. In a predetermined drum construction having walls 8 mm, the voltage dropped in a cyanide-zinc electrolyte having a conductance of 260 mS is 0.2 volts for an opening diameter of 6 mm. This voltage drop rises to 0.3 volts when the opening diameter is substantially 4 mm. When the perforation or opening diameter is substantially 2 mm, the voltage drop rises to 1.0 volts, and increases to 3.0 volts when the opening or perforation diameter is 1 mm.
The voltage drop is, furthermore linearly dependent upon the length of the cylindrical openings or perforations, and consequently upon the thickness of the wall or covering of the casing. In order to achieve substantially negligible voltage drop and therefore high current consumption, it is essential to select perforations or openings having a maximum diameter, and to locate such perforations side-by-side as close as possible. The size and shape of the parts are essential from the viewpoint of the diameter of the perforations or holes, since these parts may slip through the openings or holes or adhere to the internal walls of the perforations, when the diameters are made too large. The density or close spacing of the perforations, on the other hand, is determined by the static strength of the material from which the drum casing is fabricated.
The surface condition of the internal casing is of importance, particularly from the viewpoint of flat parts. To avoid the adherence of flat parts to the interior surface of the drum, this interior surface is fabricated of uneven or irregular shape, in different ways, in accordance with the present state of the art. Thus, the interior surface is either serrated, or perforations are partially sunk into the surface. Such resultant serrations or perforations on the interior surface, require a predetermined spacing so as to form the desired irregularity or unevenness of the inner surface of the drum. Thus, a predetermined and sufficient spacing of the perforations from opening to opening is necessary in order to achieve the desired irregularity.
It is, however, not possible to increase the current consumption of such galvanization or plating drums, due to the limitations imposed by the static structural requirements associated with the irregular or uneven interior surface caused by the serrations or perforations. Thus, whereas it would be desirable to increase the current consumption with such drums, it is not possible to do so because the spacing of the perforations are a limiting factor.
For the purpose of avoiding the disadvantages enumerated above, it was proposed to use a screen-like synthetic fabric for gauze material for the drum casing. However, drums fabricated of such screen-like casing are suitable only for treating light-weight parts, since the fabric or similar material is easily destroyed during use and operation. Thus, parts made of plastics, for example, can only be processed in the drum, when of substantially small dimensions.
In another proposed arrangement, it was suggested that the drum wall has inserted into it, so-called sieve plugs. Such a design corresponds to injection-molded or pressed plastics plugs provided with a sieve-shaped perforation. With prolonged usage, such plugs could then be readily exchanged, after having become worn out. The disadvantage of the preceding design, however, is mainly the comparatively rapid erosion of the sieve plugs, rather than the gaps prevailing between the individual sieve plugs, and which cannot be perforated.
Accordingly, it is an object of the present invention to avoid the disadvantages enumerated above, by providing a drum with maximum perforation density of the casing surface.
It is another object of the present invention to provide a drum arrangement of the foregoing character, which may be simply fabricated and economically maintained.